Sensors and other means for measurements are often connected to large fibre-reinforced structures such as parts for wind turbines, ship hulls, parts on aircrafts, etc. This includes, for instance, strain gauges for measuring the loads on the structure and its response, devices for temperature or pressure measurements, GPS receivers, lights, lightning conductors, data registration units, etc. The application of such devices or sensors then also naturally in most cases requires the guiding of elements for their functioning such as electrical wires, optical fibres, cables or the like going from somewhere practical in the structure to where the devices or sensors are placed. For instance, an optical fibre running along the length of a blade for a wind turbine being connected at its ends to light emission and receiving equipments placed near the root of the blade.
All these different elements mentioned above are often partly or totally embedded in the fibre-reinforced structure. One reason for this is that the bonding to the fibre-reinforced part in this way is far stronger than when fastened externally onto the structure by e.g. mechanical means or glue. Also, embedding can be advantageous for aerodynamically reasons. Furthermore, the element is in this way ‘wrapped’ by the fibre-reinforced structure and is thus kept well protected and safe.
It is, however, a problem when the element is to be connected to another part and thus must protrude from the fibre-reinforcement in some way to be accessible from the outside. In the marine industry it is practice to simply pull out the part of the element that needs to be accessible—typically the end—through the top layers, the injection layer and the vacuum foil before the injection of the resin into the part. However, this unavoidably reduces the quality of the injection of the resin and thus the overall quality of the fibre-reinforced structure. Furthermore, the element is easy to damage by this handling and is vulnerable during the injection, thus increasing the cost of the production and the end-product as well as increasing the risk of a malfunctioning element which is difficult or impossible to repair as the element is embedded in the structure.